Clock towers are a specific type of building which houses a turret clock and has one or more clock faces on the upper exterior walls. Many clock towers are freestanding structures but they can also adjoin or be located on top of another building.

Clock towers are a common sight in many parts of the world with some being iconic buildings. One example is the Elizabeth Tower in London (usually called "Big Ben", although strictly this name belongs only to the bell inside the tower).

Definition

There are many structures which may have clocks or clock faces attached to them and some structures have had clocks added to an existing structure. According to the Council on Tall Buildings and Urban Habitat a building is defined as a building if at least fifty percent of its height is made up of floor plates containing habitable floor area. Structures that do not meet this criterion, are defined as towers. A clock tower historically fits this definition of a tower and therefore can be defined as any tower specifically built with one or more (often four) clockfaces and that can be either freestanding or part of a church or municipal building such as a town hall. Not all clocks on buildings therefore make the building into a clock tower.

The mechanism inside the tower is known as a turret clock. It often marks the hour (and sometimes segments of an hour) by sounding large bells or chimes, sometimes playing simple musical phrases or tunes.

History

Presumably the first depiction of a medieval central European clock tower (without the actual turret clock) in the 13th century by Villard de Honnecourt, entitled: "cest li masons don orologe" ("this is the house of a clock")

Although clock towers are today mostly admired for their aesthetics, they once served an important purpose. Before the middle of the twentieth century, most people did not have watches, and prior to the 18th century even home clocks were rare. The first clocks didn't have faces, but were solely striking clocks, which sounded bells to call the surrounding community to work or to prayer. They were therefore placed in towers so the bells would be audible for a long distance. Clock towers were placed near the centres of towns and were often the tallest structures there. As clock towers became more common, the designers realized that a dial on the outside of the tower would allow the townspeople to read the time whenever they wanted.

Al-Jazari Castle clock

Al-Jazari constructed an elaborate clock and described it in his Book of Knowledge of Ingenious Mechanical Devices in 1206. It was about 3.3 metres (11 feet) high, and had multiple functions alongside timekeeping. It included a display of the zodiac and the solar and lunar paths, and a pointer in the shape of the crescent moon which travelled across the top of a gateway, moved by a hidden cart and causing automatic doors to open, each revealing a mannequin, every hour.[4][5] It was possible to re-program the length of day and night daily in order to account for the changing lengths of day and night throughout the year, and it also featured five robotic musicians who automatically play music when moved by levers operated by a hidden camshaft attached to a water wheel. Other components of the castle clock included a main reservoir with a float, a float chamber and flow regulator, plate and valve trough, two pulleys, crescent disc displaying the zodiac, and two falcon automata dropping balls into vases.[6]

Line (mains) synchronous tower clocks were introduced in the United States in the 1920s.

Taller buildings have had clock faces added to their existing structure such as the Palace of Culture and Science in Warsaw, with a clock added in 2000. The building has a roof height of 187.68 m (615.7 ft), and an antenna height of 237 m (778 ft). The NTT Docomo Yoyogi Building in Tokyo, with a clock added in 2002, has a roof height of 240 m (790 ft), and an antenna height of 272 m (892 ft).

The Abraj Al Bait, a hotel complex in Mecca constructed in 2012, has the largest and highest clock face on a building in the world, with its Makkah Royal Clock Tower having an occupied height of 494.4 m (1,622 ft), and a tip height of 601 m (1,972 ft).[12] The tower has four clock faces, two of which are 43 m (141 ft) in diameter, at about 400 m (1,300 ft) high.[13]

^"National Register of Historic Places Inventory - Nomination Form". (archive) National Park Service. page 10. Retrieved November 9, 2017. "The statue was … hoisted to the top of the tower in fourteen sections in 1894."

^""History of City Hall: 1886-1890". (archive) Retrieved November 9, 2017. "1889: Mayor Fitler moves into completed offices on west side."